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### Meaning of the Words Compass and Protractor

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Date: 08/17/99 at 22:45:01
From: Heather Bugbee
Subject: Compasses and protractors

Dear Dr. Math,

Why is a compass called a compass when it protracts and retracts, and
why is a protractor called a protractor when it is used to measure
degrees? I know this is not really a high school math question, but it
intrigues me a great deal.

Heather Bugbee
```

```
Date: 08/18/99 at 13:13:31
From: Doctor Peterson
Subject: Re: Compasses and protractors

Hi, Heather. This is not exactly a math question, but I like to talk

The word "compass" means "to go around, encircle"; it originally meant
"to measure" by pacing (passus). Since a compass "goes around," this
makes some sense.

"Protract" originally meant "to drag out, lengthen." How is that
related to what a protractor does? My dictionary gives one definition
as "[surveying] To draw to scale by means of a scale and protractor."
I suspect that because scale drawings or maps make heavy use of angles
(remember the AAA similarity theorem: a scale drawing is similar to
the original), the protractor was originally thought of as a tool for
protracting in this sense.

Words don't have to make sense to be used, but I think we can see at
least a little sense in the history behind these words.

- Doctor Peterson, The Math Forum
http://mathforum.org/dr.math/
```
Associated Topics:
Middle School Definitions

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